> I would like to throw out something for discussion that I see may become > an issue within the lifetime of many here. > I remembered reading > an interesting article on quantum computers which had said that quantum > computers could possibly prove the many-worlds hypothesis in physics. At > the time,I could not find the article. I finally found it. It was from > Discover.... > [etc.]

and Joel Cannon replied:

> 1. I am not familiar with the article (and at the start of a semester> will not become familiar with it). However, the statement that a> quantum computer that worked successfully would requre acceptance of> the many-worlds seems dubious.

You are being too kind.
I would say that the statement was just plain wrong.

> What is needed to provide evidence is a> situation where the two pictures provide conflicting> predictions. Since the yet-to-be-built computer operates using the> equations of quantum mechanics which are common to any interpretation,> a one-world situation would give the same answer.

Exactly right. Bell is rightly praised for being clever enough to think
of an experiment in which "standard" quantum mechanics and local
hidden-variable theories gave different predictions. As far as I know,
the standard "Copenhagen" interpretation, the many-worlds interpretation,
and various non-local hidden-variables interpretations
all give the same predictions for experiments. This quantum-computation
example is no different.

The "10^500 computations" claim is a canard, as two real-world analogies
should illustrate. You can build an "analog computer" (with capacitors,
resistors, inductors, amplifiers) to solve certain differential equations
much faster than the fastest digital computers. Not long ago, someone
solved a combinatorics problem by very clever application of organic
chemistry --- allowing the molecules to sort through all possible
combinations faster than a computer could. In both cases, it's not
a question of "computing power," it's a question of cleverly designing
a physical system to mimic a difficult mathematics problem.

If someone knows of a proposed experiment where the many-worlds
interpretation REALLY makes a different prediction from the standard
interpretations, I'd be very interested.

George Murphy intriguingly wrote:

> 1) Other proposals have been made for experiments to support the Many> Worlds Interpretation (MWI) of quantum theory. E.g., David Albert's> "How to Take a Photograph of Another Everett World", pp. 498-502 in> Greenberger (ed.) NEW TECHNIQUES AND IDEAS IN > QUANTUM MEASUREMENT THEORY (NY Academy of Sciences, 1986).

Thanks for the reference. If you have a summary lying around, could
you e-mail me a copy? Thanks.

Quantum theories of mind have always struck this physicist and
neuroscientist as (o.k., now I'll use the word) dubious. But let's
assume for the moment that the brain uses quantum principles
for self-awareness. Let's also give many-worlds interpretation the
benefit of the doubt. Even granting these two, we still don't
know whether or not really important personal decisions are ANYTHING
at all like a "quantum measurement." So, IMO, those intriguing
questions about the theological implications of "many-worlds decisions"
take us beyond science-and-faith into fantasy-and-faith --- a topic
which I (like J.R.R. Tolkien, C.S. Lewis, Glenn, and George) think is
worth pursuing occasionally, just so long as we know where we are.